[$] 5.1 Merge window part 2

By the time that 5.1-rc1 was released and
the 5.1 merge window ended, 11,241 non-merge changesets had
been pulled into the mainline repository. Of those, just over 5,000 were
pulled since the first 5.1 merge-window
summary. It often happens that the biggest changes are pulled
early, with the emphasis shifting to fixes by the end of the merge
window; this time, though, some of the most significant features were saved
for last.